Battery chargers are used to charge batteries of electronic appliances, such as portable computers, cellular telephones, pagers, etc. When used in connection with very small portable electronic devices, such as cellular telephones and pagers, it is preferable that the battery charger device be as small and portable as possible.
Battery chargers are known that use an ON-OFF control whereby the power source is alternatively connected and disconnected in order to generate an average charging current for the battery. This type of battery charging system is generally restricted to a single average value of charging current determined by the external power supply.
A need exists in the marketplace for a battery charging system which is low cost and retains the multi-chemistry performance advantages of a conventional switch mode power conversion system, but can be implemented in a miniature form without the use of bulky energy storage components. In addition, it is desirable to provide a switch mode power conversion type battery charger that can operate at very low switching frequencies and switching speeds, and thereby minimize electromagnetic interference (EMI) in sensitive receiver circuitry of the host device.